Forgot to install a vapour barrier behind plasterboard

[Jimmy3d0]

Hi people,
I recently bought an unfinished 'new build' house and have nearly done all the work to completion and am currently trying to get the building Control Officer to sign it all off. I have done alot of the work myself including converting the loft into a warm roof for clean dry 'Storage' purposes, I had a bit of a break from it all over the winter and focused on my work but then a few weeks ago got the inspiration to complete the loft as I need it done to get signed off due to the fact that the SAP report and EPC have factored in that I have 100mm of Celotex in the roof between the rafters, after a few days of horrible dusty work fitting all the Celotex I was very keen to get the plaster board up so I could seal in all that dust and clean up once and for all, so I spent a few days plasterboarding it all out but totally neglected to either put up a Vapour barrier or use foil backed plasterboard, and I even got as far as skimming it all out as I have learnt plastering, then I emailed Building Control who immediately reminded me about the Vapour barrier (or lack of) and told me to ask Celotex technical support if I needed one or not. Obviously Celotex said that I would need a Vapour Barrier but said that there was no technical reason why it couldn’t be below the plasterboard because it just has to be on the ‘warm side’ of the insulation and continuous. So I could just batten up a sheet of polythene as a vapour barrier and cover all my lovely plastering to satisfy BC but as I was actually trying to make a room that was for all intents and purposes the same as a loft conversion (I also have two velux’s and have first fixed wiring for lights etc) without a proper stairwell though because it will never be an official conversion due to height restrictions etc.. Anyway this got me googling etc and I saw another topic on here where someone had done the same but had rectified the mistake by using vapour control paint (not inspected by BC though), so I have researched these and found some good ones but the BCO has told me that if I use a paint then I will need to show him documentation that shows it is up to the job and independently tested etc.. The problem I am having with this is that the Celotex guy advised me this ;
I would suggest that any vapour control layer (whether a physical membrane or a paint on sealant) should have a minimum vapour resistance of 250 MNs/g. This stands for Meganewton seconds per gramme.
This would be the equivalent of a 500 gauge polythene membrane which is equivalent to 125 microns. You could speak to manufacturers of paint on sealants and see if they can give you the performance of their product in this way.
In a way you do not need a given figure, you just need to get the manufacturer state that the product is suitable to form a vapour control layer.

But I am finding it hard to equate this to what is actually written on the literature that is published with such products they all seem to be rated to the USA standard which is different and is called a ‘Perm’ rating for example in America, vapour control layers must be 1 perm or less, and the paints I have found are usually 0.6 perms so should be fine but I can’t find a converter and I have found that as a rough guide a membrane is about 125 microns ei the acceptable 250MNs/g but the paints seem to be about 25 MNs/g and the Bostic paint http://www.bostik.co.uk/constructio...pour-Barrier-Coating-ET-150/298/technicalData which seems so promising says it is; (0.034 g/sMN) (0.6 perm) at 1 mm whatever that means!!!???

And the ICI one http://www.duspec.com/DuSpec2/produ...Id=21&productCode=1060&documentType=datasheet says this ;

To be effective, a product must have a perm rating of less than 1.0, as set forth by the Federal Housing Administration Minimum Property Standards.
ICI PREP & PRIME Vapor Barrier is specifically formulated to provide a perm rating of 0.6 when applied at a coverage rate of 400 sq ft/gal (10 m2/L) to smooth surfaces.
I just can’t work out what that means or if it will comply with UK building regs more specifically satisfy my very fussy BCO it looks to me as though these paints are fine as 0.6 perms is ok in the USA so is probably ok here, but if it only equated to 25MNs/g then it is ten times less effective that the polythene sheeting so not what Celotex seem to think I need..
If anyone can shed any light on this or knows of a paint or sealant that is definitely suitable for use in place of a polythene membrane then I would really appreciate your advice as I just cannot face pulling down all my skimmed plasterboard and re-doing it all and it is already very limited for height so another layer of plasterboard wouldn’t work and I would hate to have polythene up as it might very occasionally get used as a spare room etc so polythene just wouldn’t work and would probably end up being taken down anyway!!
Anyone know the answer?

 

[AronSearle]

25MNs/g then it is ten times less effective that the polythene sheeting so not what Celotex seem to think I need

This may not be to much help, as it's a bit out of my area.

What you need to determine is what level of vapour resistivity you need, the 250 gauge that polythene provides is just standard, and not necessary what you need. Celotex probably did a condensation check analysis with 250 gauge and it passes, that's not to say lower gauges won't also pass.

You can download a free trial version of www.builddesk.co.uk

Wack your layers into the programme, and put in your VCL layer as the paint and input the value for the paint given, it will then tell you if there is a condensation risk (A pass or a fail).

Make sure it's a full pass, and not a semi pass (some condensation in winter but dries in summer, a full pass is NO condensation).

 

[Jimmy3d0]

Thanks Aron,

It seems that my BCO just likes making me jump through hoops! After doing some serious research over the weekend into vapour barrier paints, damp proof paints (which usually double as vapour barriers), liquid tanking membranes/paints etc... and researching in depth into building regulations on this topic and the relevant British standards relating to it, I decided that the paints sounded like they were definately up to the job as some od the paints esp the damp proof ones are tested to perform as DPM's and even pond liners and all sorts of uses in the building industry like damp proofing cellars etc.. so I set about trying to get the relevant specs and data and indipentant test results from the manufactures but none of the damp proof paint suppliers could help with that much so I went back to standard Vapour barrier paints, and rang Bostic to ask them about their http://www.bostik.co.uk/construction/product/idenden/Sprayable-Vapour-Barrier-Coating-ET-150/298 The guy there was very helpful and said that I was the forth person this month to have asked him about this exact same inquiry (it seems like lots of people forget to put up a VCL behind the plasterboard, or don't know they need one until BC pick up on it!!) and becuase there is a good data sheet with this product I felt confident emailing my BCO with these facts and asking for his approval...
My BCO then decided that actually what he needed was not for the manufacturer to provide me with independent test results as he had previously stated but that he just wanted confirmation from Celotex that this would be ok to use in conjunction with their product in this setting. So even though Celotex had basically already told me this would be fine *see above* I emailed them again just to humour my BCO and of coarse they said it was fine as long as the manufacturer states that is is suitable for this purpose.. So I ordered the Bostic ET-150 indenden stuff. From looking at what they all do though I would have happily used this kingfisher stuff http://www.kingfisheruk.com/item_63w5_damp_guard_-_damp_proof_paint#63w10 or this Technoseal stuff http://www.twistfix.co.uk/products/damp-proofing-cream/damp-proofing-paint-product.html but as I say, they wouldn't commit to what MNs/g value their products had as they were more aimed as damp proofing although they definitely are VCL's too and pretty good ones at that as the Technoseal is even a (tested) radon barrier so surely would stop water vapour..

Any way that is the solution I have come up with and I am going to paint a normal soaker coat (or two) of normal emulsion (or primer) on first to give the Plaster something to soak up as I don't want to waste any of the expensive VCL paint (£75 for 10litres) by it being sucked into the plaster!!

Thanks for your advice btw Aron I downloaded that very useful buildDesk software and used it as you suggested.. the funny thing was that it failed as it is now because of the interstitial condensation but passed (total pass) with a coat of gloss paint so it just goes to show, (as other people say alot about this) that paint or several past layers of paint actually do form a very effective VCL.

So anyway I hope my experience and solutions are now helpful to the next person searching for this topic in trepidation that there BCO is going to make them rip down all their pain stakingly installed plaster board to put up a VCL it seems that the Vapour barrier paints on the market are fine (although Gyproc wouldn't say that their Gyproc Drywall sealer was upto it) and perfectly good enough as a VCL and more importantly acceptable to pass an inspection by the dreaded BCO!!

 

[freddiemercurystwin]

You build on a Notice or ignore the drawings then you have to know your stuff plain and simple. No good complaining about the BCO.

 

[Jimmy3d0]

Hi Freddie, I bought the house as a new build that wasn't finished and there are no detailed plans just sketches, my budget dictates that I do alot of the work myself so I am trying my best to get through it and satisfy BC. I have posted this topic more because I was looking for advice on how to rectify the mistake I made and now to help others who made the same mistake... But the BCO has made this issue much more stressful and complicated by changing his mind about what he will accept and what he wont, I am quite happy that it was my mistake and that I need to build to building regulation standards, but if you read my posts you will notice that the BCO totally changed his mind about what documentation he required regarding the VCL paint that I used and therefore wasted hours of my time because I spent hours researching and trying to find a paint that was independently tested etc..Then for him to say that as long as Celotex said it was ok then is was, which Celotex had already done and which I had already emailed him.. Ive got nothing against BCO's but this one seems to constantly miss information I send him in emails and is always finding new hoops to make me jump through when he could just give me a list of what needs doing to finish the house to his satisfaction and let me get on with it. You can guarantee that as soon as this is all sorted and I ask him to issue me with the signing off certificate he will notice something else that he is not happy with that he should have noticed 12 months ago or 3 months ago and waste yet more of my time, simply because he doesn't inspect the house thoroughly enough when he comes and doesn't read my emails properly. Sometimes its the other way round for instance he has tried to re-inspect my disabled WC twice and both times I had to remind him that he has already accepted it!? Honestly if you met him you would understand.

 

[freddiemercurystwin]

he could just give me a list of what needs doing to finish the house to his satisfaction and let me get on with it.

That's the common misconception, BC are not contracted to do do that, its up to you to provide a compliant development.